GSM网络详解：协议、术语与实施指南

5星 · 超过95%的资源需积分: 0 7 浏览量更新于2024-08-02 收藏 5.47MB PDF 举报

《GSM网络：协议、术语与实现》是一本由Gunnar Heine所著的深入讲解GSM通信技术的优秀参考书籍，专为初学者和有经验的专业人员设计。本书作为Artech House移动通信图书馆的一部分，详细阐述了GSM（全球系统对于移动通信）的核心组成部分，包括其底层协议、专业术语以及实际应用的实施方法。 GSM是全球广泛使用的第二代移动通信标准，它采用的是时分多址（TDMA）和频分多址（FDMA）技术的结合，为移动电话提供高质量的语音通信服务。在书中，Heine教授从基础概念出发，涵盖了GSM系统的各个方面，如： 1. **网络架构**：介绍了GSM网络的组成部分，包括基站子系统（BSS）、移动交换中心（MSC）、拜访位置寄存器（VLR）和归属位置寄存器（HLR），以及它们之间的交互作用。 2. **空中接口**：着重讲述了GSM的调制解调技术，如GMSK（Gaussian Minimum Shift Keying）调制，以及错误控制编码（如CRC和交织）的重要性。 3. **信令协议**：对GSM的信令系统进行解析，如七号信令系统（No.7 Signaling System），它在移动通信中负责承载用户呼叫建立、位置更新和数据传输等操作。 4. **安全和加密**：GSM采用A5算法来保护通信的安全性，包括鉴权码和加密机制，确保用户数据的保密性。 5. **无线资源管理**：讨论了如何有效地分配和管理频率、功率和时隙，以支持大量用户的并发连接。 6. **终端设备**：介绍了移动电话的工作原理，包括基带处理单元（BBU）、射频前端和用户接口（UI）等关键组件。 7. **标准化和互操作性**：GSM是国际电信联盟（ITU）制定的标准，书中解释了标准的制定过程和不同运营商间如何实现网络间的无缝对接。 8. **实施与案例研究**：书中不仅理论知识丰富，还包含实战案例，帮助读者理解GSM技术在实际环境中的应用和优化策略。通过阅读这本书，无论是想要了解GSM技术的入门者还是希望深化理解的专业人员，都能收获丰富的知识，掌握这一全球移动通信的基础。书中提供的全面内容和实用指南，使得《GSM网络：协议、术语与实现》成为通信工程和技术领域不可或缺的参考资料。

BSC takes care of all the central functions and the control of the

subsystem, referred to as the base station subsystem (BSS). The BSS

comprises the BSC itself and the connected BTSs.

1.2.2.5 Transcoding Rate and Adaptation Unit

One of the most important aspects of a mobile network is the effec-

tiveness with which it uses the available frequency resources. Effective-

ness addresses how many calls can be made by using a certain

bandwidth, which in turn translates into the necessity to compress

data, at least over the Air-interface. In a GSM system, data compres-

sion is performed in both the MS and the TRAU. From the architec-

ture perspective, the TRAU is part of the BSS. An appropriate

graphical representation of the TRAU is a black box or, more symboli-

cally, a clamp.

1.2.2.6 Mobile Services Switching Center

A large number of BSCs are connected to the MSC via the

A-interface. The MSC is very similar to a regular digital telephone

exchange and is accessed by external networks exactly the same way.

The major tasks of an MSC are the routing of incoming and outgo-

ing calls and the assignment of user channels on the A-interface.

1.2.2.7 Home Location Register

The MSC is only one subcenter of a GSM network. Another subcen-

ter is the HLR, a repository that stores the data of a large number of

subscribers. An HLR can be regarded as a large database that adminis-

ters the data of literally hundreds of thousands of subscribers. Every

PLMN requires at least one HLR.

1.2.2.8 Visitor Location Register

The VLR was devised so that the HLR would not be overloaded with

inquiries on data about its subscribers. Like the HLR, a VLR contains

subscriber data, but only part of the data in the HLR and only

while the particular subscriber roams in the area for which the VLR

is responsible. When the subscriber moves out of the VLR area,

the HLR requests removal of the data related to a subscriber from the

VLR. The geographic area of the VLR consists of the total area cov-

ered by those BTSs that are related to the MSCs for which the VLR

provides its services.

6 GSM Networks: Protocols, Terminology, and Implementation

TRAU

MSC

HLR

VLR

1.2.2.9 Equipment Identity Register

The theft of GSM mobile telephones seems attractive, since the iden-

tities of subscribers and their mobile equipment are separate. Stolen

equipment can be reused simply by using any valid SIM. Barring of a

subscriber by the operator does not bar the mobile equipment. To

prevent that kind of misuse, every GSM terminal equipment contains

a unique identifier, the international mobile equipment identity

(IMEI). It lies within the realm of responsibilities of a network opera-

tor to equip the PLNM with an additional database, the EIR, in which

stolen equipment is registered and so can be used to bar fraudulent

calls and even, theoretically, to track down a thief (by analyzing the

related SIM data).

1.3 The Focus of This Book

This book describes briefly the GSM subsystems, their structure, and their

tasks. However, the focus of this book lies not on the GSM network elements

themselves but on the interfaces between them.

Among others, the following issues will be addressed:

•

What signaling standards and what protocols are used to serve connec-

tion requests by mobile subscribers?

•

How are the various interfaces utilized?

•

What happens in case of errors?

•

Although GSM uses available signaling standards, where are the GSM

specific adaptations?

One has to remember that most of the signaling is necessary to support

the mobility of a subscriber. All messages of the area mobility management

(MM) and radio resource management (RR), in particular, serve only that

purpose. Only a fraction of the exchanged messages are used for the connec-

tion setup as such, and those are all the messages that are related to call

control (CC).

A presentation of the Open System Interconnection (OSI) Reference

Model is mandatory in a book in which the focus is on signaling.

Another focus of the text is on the application of the various protocols for

error analysis. Which error indication is sent by the system and when? How is

such an indication interpreted? What are the potential sources of errors?

Introduction 7

EIR

A word on coding of parameters and messages should be added here:

Coding of message types and other essential parameters are always included.

However, because this book has no intention of being a copy of the GSM Rec-

ommendations, it deliberately refrains from providing a complete list of all

parameters of all interfaces.

The value of protocol test equipment for error analysis and routine testing

is indisputably high, but what help do programs for automatic analysis provide?

Those questions will be answered as well.

A large part of this book is taken up by a glossary, which provides descrip-

tions of all abbreviations, terms, and processes that a reader may confront dur-

ing work on GSM.

1.4 Signaling

The main focus of this book is on the signaling between the various network

elements of GSM. The questions arise of what signaling actually constitutes

and what it is used for. Although we do not want to go back to the basics of

telecommunications to answer those questions, a number of basic explanations

do seem necessary.

1.4.1 What is Signaling?

Signaling is the language of telecommunications that machines and computers

use to communicate with each other. In particular, the signals that a user enters

need to be converted to a format that is appropriate for machines and then

transmitted to a remote entity. The signals (e.g., the identity of a called party)

are not part of the communication as such, that is, they are not a payload or a

revenue-earning entity.

Signaling is comparable to the pilots and the flight attendants on an

airplane. The crew members are no “payload,” but they are necessary to carry

the payload. Another, perhaps more appropriate, illustration is to consider the

now almost extinct telephone operator, whose function it was to carry out the

signaling function and switching of a telecommunications system by connect-

ing cables between the appropriate incoming and outgoing lines.

1.4.2 How is Signaling Performed?

When calls were set up manually, signaling consisted mostly of direct current

impulses, which allowed a central office to determine the dialed digits. Some

8 GSM Networks: Protocols, Terminology, and Implementation

readers may still remember the rotary telephone sets, in which the impulses

were created mechanically by the spin of the rotor. The situation changed com-

pletely with the entry of computer technology into telecommunications. The

microchip utilized by telecommunications opens today, at the end of the

twentieth century, a multitude of new signaling functionality, which were

unthinkable even 20 years ago. Computers are the backbone of modern tele-

communications systems.

This new technology makes mobile communications possible in the first

place. The signaling requirements of modern mobile systems are so vast that the

former technology would not have been able to manage them. Computeriza-

tion, however, did not change much of the principle. As in the old days, electri-

cal or optical signals are sent, over an appropriate medium (typically serially)

and interpreted by the receiver. What did change is the speed of the transmis-

sion. The progress in this area has been exponential.

The smallest unit of a signal is called a bit and can, for example, be repre-

sented by an electric voltage, which a receiver can measure during a specified

period of time. If the receiver measures the voltage as “low” over the specified

time period, it interprets the value as a 0. If the voltage is “high,” the receiver

interprets the value as a 1. It does not matter which level represents which

value, so long as both the sender and the receiver agree on which is which.

A sequence of bits allows the coding and sending of complex messages,

which, in turn, allows a process to be controlled or information to be conveyed.

The result is a bit stream, as shown in Figure 1.3.

Pulse code modulation (PCM) is the worldwide process for transmission

of digital signals. PCM is used to transmit both signaling data and payload.

PCM is categorized into hierarchies, depending on the transmission rate. The

PCM link of 2 megabits per second (Mbps) (one that is referred to frequently

in this book) is only one variant of many. By utilizing a time-division

Introduction 9

bit value = 0

U(low) U(high)<

bit value = 1

U(high) U(low)>

time

hex

1110000 0011

}

Figure 1.3 Decoding of a bit stream.

multiplexing technique, such a 2-Mbps PCM link can, among others, be parti-

tioned into 32 independent channels, each capable of carrying 64 kilobits per

second (Kbps).

Another aspect of the change that the digital technology has enabled

reveals its advantage only after a second look. Almost all signaling standards,

like Signaling System Number 7 (SS7) and Link Access Protocol for the

D-channel (LAPD) separate the traffic channel from the signaling or control

channel. This is referred to as outband signaling, in contrast to inband signal-

ing. In the case of inband signaling, all the control information is carried within

the traffic channel. Although outband signaling requires the reservation of

a traffic channel, it makes a more efficient use of resources overall. The

reason for that lies in the reduced occupation time of the traffic channel,

which is not needed during call setup. Both call setup and call release can be

carried out for many connections via one control channel, since signaling

data use the resources more economically. One 64-Kbps time slot out of a

2-Mbps PCM link typically is used for signaling data; a call setup consumes

about 1 to 2 Kbps.

1.4.3 What is Signaling Used For?

The main task of signaling is still to set up and to clear a connection between

end users or machines. Today, constantly new applications are added. Among

them are automated database accesses, in which telecommunications systems

call each other and which are fairly transparent to a caller, or the wide area of

supplementary services, of which only call forwarding is mentioned here as an

example. The glossary provides a list of all GSM supplementary services.

1.5 Representation of Messages

When working with protocol test equipment and in practical work, message

names usually are abbreviated. Most GSM and ITU Telecommunication

Standardization Sector (ITU-T) Recommendations list the well-defined

abbreviations and acronyms, which this book also uses to a large extent. The

complete message names and explanations can be found in the respective

chapters.

Since a picture often expresses more than a thousand words, this book

contains a large number of figures and protocol listings. The various messages

illustrated in the figures show parameters, which are formatted per interface

and are presented as shown in Figures 1.4(a) through 1.4(e).

10 GSM Networks: Protocols, Terminology, and Implementation

剩余416页未读，继续阅读

ab339

粉丝: 0
资源: 3

GSM网络详解：协议、术语与实施指南

GSM.Networks..Protocols.Terminology.and.Implementation

Tcp/Ip: Architcture, Protocols, and Implementation With Ipv6 and Ip Security

[Wireless Networks and Mobile Communications-10]RFID and Sensor Networks: Architectures, Protocols, Security, and Integrations

TcpIp Architcture, Protocols, and Implementation With Ipv6 and Ip Security

In-Vehicle Networking: Protocols, Challenges, and Solutions

computer networking ： principles protocols and practice

Network Routing: Algorithms Protocols and Architectures

应用密码学(协议算法与C源程序) 原书名：Applied Cryptography:Protocols,Algorithms,and Source Code in [第二部分 共两部分]

ISO IEC TS 27034-5-1 Information technology - Application security- Part 5-1：Protocols and application security controls data structure, XML schemas - 完整英文版（83页）.pdf

AN平台中端人证及访客V1.0项目DSP设计文档_Network Protocols Analysis and Implementation.zip

最新资源

应用密码学(协议算法与C源程序) 原书名：Applied Cryptography:Protocols,Algorithms,and Source Code in [第二部分共两部分]